In many areas of medical treatment, it would be beneficial for a medical practitioner to be able to visualize a region for which treatment is contemplated and to accurately simulate the contemplated treatment. By visualizing the effect of the simulated treatment and altering the proposed treatment to optimize the results in a virtual setting, results can be improved and risks associated with the actual treatment can be reduced. This is particularly true in the case of invasive procedures such as surgery, biopsies and prosthesis implantation. The virtual setting would serve both as a tool for the guidance for actual treatment and as a “gold standard” for evaluation of the actual treatment and for follow up management.
The ear is a specialized organ for which the computer aided treatment planning is expected to play a valuable role. The ear is an internal organ that is difficult to examine because it is encased in the temporal bone. The ear also contains important anatomic structures, including the hearing bones (ossicles), inner ear organs of hearing and balance, and facial nerve. Congenital aural atresia (CAA) is a congenital developmental anomaly of the middle ear that manifests with varying degrees of external auditory canal stenosis or atresia, ossicular derangements, poorly developed mastoid and tympanic cavities. This disease results in conductive hearing loss which can be severe. In some cases, however, CAA can be treated surgically. However, because of the complex anatomy of the ear and the risks associated with this surgical procedure, such as facial paralysis, thorough surgical planning is required to assess and maximize the likelihood of successful surgery.
Preoperative imaging, such as by computerized tomography (CT), is considered an important element in surgical planning. Conventional two-dimensional (2D) CT images demonstrate the key anatomic structures of the ear, including the stapes, middle ear space, inner ear and facial nerve. However, the 2D CT is limited in its ability to represent the spatial relationships between these important structures. For example, an aberrant facial nerve, a retro-displaced temporamandibular joint, or a low-lying tegmen tympani might make surgical reconstruction difficult or impossible. Three-dimensional (3D) information would be very helpful for planning surgical therapy for treating congenital aural atresia and other forms of ear pathology.
Traditionally, spatial anatomical relationships could only be surmised by mentally integrating sequential 2D CT scan images. However, the advent of 3D computer graphical visualization techniques and high-resolution CT scanning now allow 3D images (either surface-based or volume-based) to be constructed from sequential scan images and be displayed on a computer screen. Three-dimensional relationships between adjacent organs can be shown by interactively manipulating these virtual organs on the screen using a mouse or some other interactive devices. Over the past decade, many applications of such techniques in a number of areas of medicine, including otology, have been explored.
The article “Three Dimensional CT Scan Reconstruction for the Assessment of Congenital Aural Atresia” by Andrews et al., which was published in the American Journal of Otology, Vol. 13, Num. 13, May 1992, discusses generating 3D computer images from 2D CT data to aid a surgical planning of CAA. This paper demonstrates that the structures of the ear can be successfully rendered to assist the surgeon in visualizing the spatial relationships among the critical structures of the ear, such as the facial nerve, mandibular condyle, the locations and thickness of the atretic plate and the like. The system disclosed by Andrews et al., provided a useful 3D image of the anatomy of the ear. However, due to the complexities of the anatomy of the ear, additional computer-aided planning and “virtual surgery” features to confirm the surgical plan would also be desirable.
Accordingly, there remains a need for improved medical treatment planning tools for optimizing the procedures and for evaluating the results.